Hugh Johnson, the venerable English wine writer, had just arrived in New York City on a trip he tries to make every year, especially in the fall when “the elms start to fire up.”

As is his custom, he visited old friends, took in a few restaurants — Le Coucou, the new Rouge Tomate Chelsea and an old favorite, Jean-Georges Vongerichten’s JoJo. He stopped at a few museums and strolled through Central Park, where he indulged another passion that is as dear to his heart as wine — trees.

Wine lovers who know Mr. Johnson through his essential books, like “The World Atlas of Wine” (in its seventh edition and now written with Jancis Robinson), may be surprised to learn that he is also a fervent student of trees and gardening. He is that rare expert who has achieved international authority on more than one subject. Beyond wine, his books include “The World of Trees” and “Principles of Gardening.”

This year’s visit held a particular resonance for Mr. Johnson. He has just published the 2017 “Pocket Wine Book,” its 40th edition. The handy annual guide has documented the state of the wine world through decades of tumultuous growth.

Mitchell Beazley, its publisher, put sales of the guides at 12 million copies worldwide, many of them no doubt well thumbed and dog-eared. Mr. Johnson’s trip included a few appearances to promote it. He would also play host at a reception at the British consul’s residence for the British Bottle Company, founded by his son, Red Johnson, to export British alcoholic beverages, including some fine sparkling wines, around the world.

The elder Mr. Johnson has always held a hallowed place for me among modern wine writers. He is the rare writer who likes to think about wine as much as drink it. With erudition, imagination and flair, he conveys scholarship while winking at the contradictions so often revealed when trying to articulate fleeting sensations with concrete language.

At least once or twice a year, I find myself going back to “A Life Uncorked,” his 2005 memoir of the bottles he’s opened and the people with whom he consumed them. It’s full of wisdom and small gems that convey more about the soul of wine than reams of tasting notes and bottle scores ever will.

With stolid determination, most wine writers fixate on telling readers what to do: buy this bottle, drink by 2020. For Mr. Johnson, wine is never so simple or so certain. It’s the questions wine raises that fascinate him and inform his conversation with what’s in the glass.

“The appellations of Burgundy are a work of art in their own right: never were so many shades of rank and meaning packed into so few words,” he writes of three young white grand cru Burgundies he’s tasting. “‘Silky, sulky, sour,’ is what I wrote in my notes, inebriated with words I fear. What are ‘crosscurrents of energy’? A switchboard? Energy, though, is the point: the quality that all good wines possess, and a few to an electrical degree.”

I visited with Mr. Johnson on a crisp fall morning, one of the first cool days of October. The leaves, sadly, would not turn for a few weeks more. We met at the Frick Collection, his favorite New York museum. Like a good bottle of cru bourgeois Bordeaux, the midrange wine that is a staple of his drinking life these days, the Frick offers a refreshing dip into greatness without demanding undivided attention or concentration.

Mr. Johnson is drawn to paintings as if they were old acquaintances, displaying the relentless curiosity and darts of observation that infuse his writings on wine. A portrait of Sir Thomas More by Hans Holbein the Younger captured his attention.

“Devastating, really,” he said of the subject. “An uncompromising saint.”

He stopped to stare at Rembrandt’s “The Polish Rider,” in which a young archer is perched atop a white horse in midtrot.

“Now, why did Rembrandt do that?” Mr. Johnson asked. “It’s so different from everything else he did.”…